When drilling an oil and gas well, one or more casing strings are installed and cemented in a wellbore as drilling progresses to increasing depths. The casing strings may provide stability to limit cave-ins in unstable formations, and may isolate the wellbore from the surrounding formation. As a result, the casing strings can seal off high-pressure zones from the surface and prevent fluid loss or contamination of production zones. The casing strings may also provide a smooth internal surface for installing production equipment.
Once the oil and gas well is no longer commercially viable, the well may be abandoned, or slot recovery may be performed to use the wellbore as a kickoff point for sidetracking and the formation of a lateral borehole. Removal of a portion of a casing string for well abandonment or slot recovery operations may include performing a section milling operation. Section mill blades are in a retracted or inactive state when the milling tool is tripped into the wellbore. Upon reaching a desired depth, the section mill blades are expanded into a radially outward, active state that engages the casing. As the milling tool and milling blades are rotated in the wellbore, the blades make a circumferential cut in the casing string. The tool string is then urged downhole while rotation continues so as to axially mill away a desired length of the casing string.